“Mass spectrometry” is a method for obtaining structural information of a molecule, by ionizing a sample including the molecule, separating the ionized molecule based on mass-to-charge (m/z), and detecting the molecular ions.
Detection of the molecular ions for determining the molecular weight using a mass spectrometer cannot afford detailed structural information for molecules such as saccharides, oligosaccharides (saccharide chains), proteins (including peptide), proteins modified by saccharides (including glycopeptides (peptide modified by saccharides)), nucleic acids and glycolipids, because of possible structural isomers having the same molecular weight and composition.
Therefore, MSn (n>1) analysis is carried out. “MSn (n>1) analysis” is an analysis method for obtaining the structural information of a molecule by the steps of ionizing a biomolecule, selecting precursor ions, detecting product ions generated by post source decay (PSD), in source decay (ISD), tandem mass and the like, or alternatively by the step of selecting precursor ions from the product ions having been generated, repeating the same measurement.
In order to carry out the MSn (n>1) analysis, it is necessary to generate a sufficient amount of parent ions ([M+Na]+, [M+H]+, [M−H]− and the like) which become the precursor ions. However, it is difficult to obtain a sufficient amount of the parent ions for the molecules originated from the biological samples, since it is hard for such molecule as-is to be ionized sufficiently. For example, when the oligosaccharide is analyzed using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), 10 pmol or more of the oligosaccharide is required. In order to solve the problem, there is proposed a method of labeling the oligosaccharide by the use of 1-pyrenebutanoic acid hydrazide (PBH) (for example, see Nonpatent Document 1). When the oligosaccharide labeled by the method is analyzed by the MALDI-TOF MS, reduction in detection limit (that is, improvement in sensitivity of MS) is recognized in comparison with an unlabeled oligosaccharide. However, in the current state, it has been insufficient to generate the parent ions to a required level for carrying out the MSn (n>1) analysis to the biological samples in sub-pmol level.
Nonpatent Document 1: Sugahara, D. Et al., Anal. Sci, 19, 167-169 (2003)
Nonpatent Document 2: Harvey, D. J., J. Mass Spectrom., 40, 642-653 (2005)
Nonpatent Document 3: Harvey, D. J., J. Am. Soc. Mass. Spectrom., 16, 647-659 (2005)